In the field of modern Point-of-Sale (POS) transaction printers, the objective is to provide simple, compact machines that are easy both to operate and to load. Axiohm Corporation, the assignee of the present invention, has pioneered the use of drop-loading paper supply rolls and clamshell receipt printers.
To save space and to provide faster transaction processing times for customers, many operations heretofore performed on separate pieces of equipment or performed after the actual sales transaction, have been combined into the POS transaction printer. One such feature permits encoding Magnetic Ink Character Recognition (MICR) symbols onto the Amount field of a customer's check presented in payment for goods or services. MICR encoding requires a high-quality, specialized printer ribbon incorporating magnetic particles which, after deposition on the check, allow magnetization and subsequent reading of the MICR characters.
In order to save space and provide easier ribbon loading in the MICR printing devices, the invention of the aforementioned co-pending U.S. patent application Ser. No. 09/130,598, proposed to provide a cassette containing a MICR printing ribbon that is both dispensed and stored upon a common rotative shaft. The compact ribbon cassette replaced cassettes having spaced-apart, individual dispensing and storage rolls that divided the dispensing and storage functions.
The aforementioned, prior application described a new style of ribbon cassette for POS printers incorporating a MICR encoder, that vertically stacked the supply roll upon the take-up roll. The supply and take-up rolls were supported upon a common shaft that was rotatively supported within the cassette housing.
The ribbon cassette had a cover plate that contained integrally formed leaf springs designed to bear upon a friction plate disposed over the wound supply-ribbon spool. These leaf springs provided biasing against the friction plate, which in turn caused frictional loading of the wound supply ribbon. The friction exerted upon the supply ribbon by the friction plate maintained a tension upon the supply roll of ribbon, so that the ribbon was kept taught as it was dispensed from the supply roll. This eliminated loosely formed intervals in the ribbon as it was dispensed.
A uniquely formed chevron, disposed adjacent the supply and take-up rolls, allowed for the ribbon direction to be reversed from the supply roll to the take-up roll and shifted the level of the ribbon from the lower supply spool to the upper take-up spool. Each roll was rotated in a counter-clockwise direction, wherein the ribbon was dispensed from the lower, supply roll, then reversed direction, and was then wound upon the upper, take-up roll.
It has been discovered that the MICR printing ribbon that glides over the ribbon level changing chevron becomes wiped of its ink, especially near the edges of the ribbon. The wiped ink may be deposited upon the chevron, and may eventually flake off. These flaked ink particles can be randomly deposited upon the print line near the MICR characters, thereby causing MICR read errors.
The present invention reflects the discovery that changing the cassette construction reduces or eliminates the possibility of flaked magnetic ink being deposited upon the printed MICR line. The improved cassette now features a chevron that is located in the post-printing portion of the cassette. Now, if any flaking occurs upon the chevron, it does so after the ribbon has passed through the print window. Therefore, the flaking becomes inconsequential with respect to the printed MICR character quality. However, the flaked ink particles must still be prevented from migrating across the cassette from the post-printing portion to the pre-printing portion. In order to prevent this migration, the pre-printing portion of the cassette is constructed so as to form a sealed chamber. This sealed chamber is created by a plastic partition disposed between the post-printing portion and pre-printing portion of the cassette.
As a further precaution against migrating ink particles, the newly designed cassette also contains a wiper pad to remove any stray ink particles from the ribbon before they and it enter the print window.
To provide substantially constant tension on the ribbon, spring fingers are molded into the ribbon cassette housing. The spring fingers, acting co-operatively with a friction plate, impose a drag on the supply ribbon pack. The spring fingers and friction plate cause the drag to remain constant, whether the supply spool is full or nearly empty. In addition, a spring-loaded idler roller located adjacent to the supply ribbon spool helps maintain proper ribbon tension as the MICR printing platen is opened and closed.